ar crashes building libgcc.a

[Andrew Cagney]

I've checked this in.  It's fairly obvious, now a testcase ....

Andrew

> 2004-04-22  Andrew Cagney  <cagney@redhat.com>
> 
> 	* cache.c (bfd_cache_close): Check for a previously closed file.
> 
> Index: cache.c